1. Field of the Invention
The present invention relates to a radio communication control apparatus and a radio communication control method for performing simultaneous transmission and reception, using the same carrier frequency.
2. Related Background of the Invention
As a transmission/reception multiplexing system in the conventional radio communication such as mobile phone, there have been employed FDD (Frequency Division Duplex) system simultaneously performing transmission and reception using different RF (Radio Frequency) carrier frequencies in uplink and downlink, and TDD (Time Division Duplex) system performing transmission and reception using the same RF carrier frequency but in different time slots for the transmission and reception (for example, refer to Japanese Patent Application Laid-open No. 2000-13858). Also, in a wireless LAN, etc., CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance) system is employed, in which communication on the same RF carrier frequency is performed after confirming, by utilizing received signal power, that no communication is being performed in the surroundings using the RF carrier frequency concerned. From the viewpoint of multiplexing the transmission and reception, CSMA/CA system uses different time segments between transmission and reception.
Meanwhile, to further improve spectrum efficiency, a simultaneous transmission and reception method is under study, in which transmission and reception are performed in the same time segment (time slot) using the same RF carrier frequency. Here, in the simultaneous transmission and reception method for simultaneously performing transmission and reception, a signal transmitted from radio equipment is undesirably received in the same radio equipment, as a coupling loop interference signal. There are two main causes of the above coupling loop interference signal: (1) an interference signal produced by a signal from a transmission RF signal processing section being leaked into a received RF signal processing section because of the incompleteness of a circulator; and (2) an interference signal produced by a transmission signal transmitted from an antenna being received by the same antenna, under the influence of propagation paths with reflection, diffraction, etc. Accordingly, studies of radio equipment are in progress to achieve simultaneous transmission and reception by eliminating interference caused by the coupling loop interference signal, using an interference canceller in the analog domain and/or the digital domain.
However, when performing simultaneous transmission and reception, a received SINR (Signal-to-Interference plus Noise power Ratio) is degraded as compared to the case of not performing simultaneous transmission and reception, even if the interference canceller is employed to cope with the influence of the coupling loop interference signal. Also, transmission quality, such as a throughput performance and a BER (Bit Error Rate) performance, in the uplink and downlink varies depending on both the received SINR, which is determined by the desired signal power and the coupling loop interference signal power in the received signal, and the interference cancelling performance in the interference canceller. Therefore, in the circumstances of a low received SINR with insufficient interference cancellation, simultaneous transmission and reception may possibly deteriorate system throughput performance to a large extent. As a result, the system throughput is degraded as compared to the case of not performing simultaneous transmission and reception, and to the contrary, spectrum efficiency may be deteriorated by the execution of simultaneous transmission and reception.